A multilink-type suspension having three or more suspension arms has been broadly used from the past in vehicles such as automobiles, and various structures have been proposed as a sub-frame structure for supporting the suspension arms.
For example, with the sub-frame structure described in Japanese Patent Application Laid-open No. 2006-347338 (Patent Document 1), separate brackets for supporting a total of five suspension arms are respectively provided on both left and right ends of a suspension cross member configured from a pair of cross members extending in a vehicle width direction and a pair of side members extending in a vehicle front-back direction. However, since numerous parts are used in this structure, there is a problem in that it is difficult to improve weight saving and productivity.
As a structure for resolving the foregoing problem, with the structure described in Japanese Patent Application Laid-open No. 2009-255902 (Patent Document 2), an upper arm supporting part and a lower arm supporting part are integrally formed with a front width direction member, and, by directly mounting the respective suspension arms on these supporting parts, reduction in the number of parts and weight saving are obtained.
In order to increase the rigidity of the sub-frame in the front-back direction, the structure described in Patent Document 2 comprises an inclination reinforcing member for connecting the upper arm supporting part and the lower arm supporting part of the front width direction member to the intermediate part of the rear width direction member.
This inclination reinforcing member basically supports the entire front width direction member. Specifically, the inclination reinforcing member reinforces the rigidity of the sub-frame in the front-back direction by covering, at both left and right ends in the vehicle width direction, a range from a top end of the upper arm supporting part to a bottom end of the lower arm supporting part of the front width direction member.
However, with the foregoing structure described in Patent Document 2, since the inclination reinforcing member covers a range from the top end of the upper arm supporting part to the bottom end of the lower arm supporting part of the front width direction member in order to reinforce the rigidity of the sub-frame in the front-back direction, the size and weight of the inclination reinforcing member inevitably increases. Thus, it is difficult to achieve the weight saving of the sub-frame. Meanwhile, if the size of the inclination reinforcing member is reduced, there is a problem in that it becomes difficult to maintain the rigidity of the sub-frame in the front-back direction.